1. Field of the Invention
The present invention relates to a control apparatus for an electric rotating machine.
2. Description of Related Art
As described, for example, in Japanese Patent Application Laid-open No. 2006-174697, there is known a control apparatus which performs model predictive control to control an electric rotating machine. This control apparatus operates as follows. First, a sequence of switch states at sampling timings k, k+1, . . . k+N−1 (N≧1) is provisionally set, and a prediction of a torque track is made for the sampling timings k to k+N. Next, a prediction of a torque track afterwards is made by extrapolation as a torque track at sampling timings k+N−1 to k+N. Next, the number of times of change of the switch state in the sequence provisionally set is divided by a number n indicative of the number of times of sampling performed until the torque predicted by the extrapolation deviates from a predetermined range. Next, a switch state at the sampling timing k of the switching sequence is determined as an actual switching state at the sampling timing k, if the quotient of the above division is the minimum of all the switching sequences provisionally set. According to the above model predictive control, the number of times of change of the switch state can be reduced.
In the above model predictive control, the quotient becomes smaller as the period of time elapsed until the torque predicted by the extrapolation deviates from the predetermined range becomes longer. Accordingly, the quotient becomes small even when the number of times of change of the switch state for the sampling timings k to k+N−1 state is large, if the number of the sampling times n is large. Hence, the above described conventional control apparatus cannot always sufficiently reduce the number of times of change of the switch state. Further, since the accuracy of torque prediction by extrapolation is not necessarily high, and accordingly the above described conventional control apparatus variably sets weighting factors used to evaluate the number of times of change of the switch state based on the inaccurate prediction of torque behavior, there is a problem in the reliability of the control.